DOW-UAP-D137, AAWSAP DIRD, State of the Art and Evolution of High-Energy Lasers, March 2010

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State of the Art and Evolution of High-Energy Laser Prepared by: Acquisition Support Division (DW0-3) Defense Warning Office Directorate for Analysis Defense Intelligence Agency AAP Person 79 Administrative Note COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one in a series of advanced technology reports produced in FY 2009 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapon System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to!AAP Person 1 AAWSA Program Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington,

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Basic Attributes of Kinetic Energy and HEL Weapons ......................................... 1 Elements of an HEL weapon ............................................................................... 2 Rod and Slab Lasers ........................................................................................... 7 Ultra-Short Pulse Lasers .................................................................................. 10 Beam Control and Atmospheric Propagation of Laser Devices.............................. 12 Brief History of DoD Laser Weapon Research ....................................................... 16 Vulnerability of Spacecraft to Laser Radiation...................................................... 22 Projection of Future HEL Weapon Capability ........................................................ 23 Sources of Further Information............................................................................ 26 Figure 1. Utility of KE and HEL Weapons ................................................................. 2 Figure 2. Elements of an HEL Weapon System........................................................ 3 Figure 3. Basic Laser Concept................................................................................. 4 Figure 4. Cylindrical Gain Generator for HF Chemical Space Based Laser ............... 5 Figure 5. Common Solid-State Lasers and Their Wavelengths ................................ 6 Figure 6. Incoherent Combination of Single Mode Lasers at the Target.................. 9

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Figure 7. Incoherent Combination of Single Mode Lasers in a Fiber Combiner ....... 9 Figure 9. Elements of the 2 kW FEL at Thomas Jeffereson National Accelerator Figure 10. HEL Weapon Basic Tracking and Pointion Controls .............................. 14 Figure 12. Typical Atmospheric Absorption and Scattering in the Infrared .......... 16 Figure 13. Army Mobile Tactical Unit .................................................................... 17 Figure 14. Air Force Airborne Laser Laboratory .................................................... 17 Figure 15. Mid-Infared Advanced Chemical Laser................................................. 18 Figure 17. The Advanced Tactical Laser C-130 Aircraft......................................... 20 Figure 18. Single Pulse Maximum Permissible Exposure ...................................... 22 Table 1. Laser Systems Irradiance Calculations ................................................... 25

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State of the Art and Evolution of High-Energy Laser The laser was invented in 1960, only 49 years ago, and (along with the light­ emitting diode) has evolved into an essential part of our modern every-day life in ways that could not have been foreseen. On the military side, there have also been incredible advances in laser and beam control technologies but no deployment of any high-energy weapons. Many concepts have been developed and pursued, only to be discarded or deferred owing to technical immaturity, expected production cost, lack of apparent utility, or logistics concerns. The most significant technical impediment to deployment may have been the large quantities of expensive and hazardous chemicals that were required by the only available high-average-power lasers. This is now changing with recent advances in electrically powered lasers (both solid-state and free­ electron lasers). As these devices mature over the next few decades, they will enable practical military weapons at power levels ranging from kilowatts to megawatts. This evolution may be somewhat slowed or limited in the United States if there are policy concerns about the use of new types of weapons or about weaponization of space. As an example, the Department of Defense developed a microwave device for crowd control, called Active Denial, which has been shown to produce temporary pain without any injury. However, DoD was precluded from deploying it owing to policy (not legal) concerns. Other countries may not exhibit similar restraint, as evidenced by the open marketing of laser-blinding weapons despite a 1980 Geneva Convention prohibiting their development or use. Space offers the ideal environment for laser beam propagation; there is no atmosphere to either attenuate or spread the beam. As a result, large distances could be bridged quickly, with range limited by the size of the transmitting telescope and the potential damage mechanisms limited primarily by the laser's output power. Initial spacecraft laser weapons are conceivable within the next 20 years, with the potential for follow-on growth in laser power and transmitting telescope size. Transmitting telescope size would be limited by the spacecraft size and competing demands for weight and volume. Laser power could grow to the megawatt range as solid-state and free­ electron laser technology matures, but the major limitation to a spacecraft's weapon capability may prove to be its ability to generate and store the energy required by the laser and to store and dissipate the resultant waste heat.

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The purpose of this report is to provide an overview of the current state-of-the-art and potential evolution of megawatt (MW) class high-energy laser (HEL) weapons. Implications for space vehicles in or beyond earth orbit will be addressed. It is rare today to find an individual who doesn't have some concept of a laser weapon. From Orson Wells's Martian invaders in War of the Worlds, who used them with chilling efficiency, to the now-classic Star Wars movies, the capabilities attributed to such devices have grown with time and with writers' imagination. While most fictional depictions of laser weapons (and many news stories) are without sound basis, these devices do offer the potential for a whole new class of weapons and capabilities which may complement (but not replace) existing kinetic energy (KE) weapons and electronic BASIC ATTRIBUTES OF KINETIC ENERGY AND HEL WEAPONS KE weapons (bullets, shells, missiles, bombs, and so forth) require a finite period of time to reach the target but are then able to destroy it instantly. They can deliver immense quantities of explosive energy and destroy large areas. This makes KE weapons most effective at engaging hardened, large, or stationary targets. Collateral damage concerns, such as a desired target next to a hospital, enemy forces near friendly forces, or a sniper target in a crowd can significantly limit the opportunity to use KE weapons. Randomly moving targets also present a challenge for KE weapons due to difficulties in predicting the target's location at the future time of arrival or in tracking the target with sufficient accuracy. High Energy Laser (HEL) weapons, by contrast, begin delivering the laser beam's